1. Field of the Invention
The present invention relates to a light emitting device, and more particularly relates to a light emitting device using a light emitting element such as a light emitting diode.
2. Background Information
Information terminal devices featuring semiconductor light emitting elements occupy an important position today as optical printers and so forth. In particular, full-color printing has become possible with the development of conductor light emitting elements capable of emitting RGB (red, green, and blue) at high brightness levels for all colors. For example, there is a known light emitting device in which a red LED, a green LED, and a blue LED are each mounted on a lead frame, and these lead frames are insulated a specific distance apart. With a light emitting device such as this, however, the lead frames have to be kept apart so they do not touch each other, so the elements have to be disposed away from each other, and this is a problem in that color mixing of the light suffers.
To deal with this problem, a light emitting device has been proposed in which independent lead frames are insulated from one another so that voltage is applied individually to a red LED, a green LED, and a blue LED, and an electrode formed on the bottom of the red LED and a insulating substrate formed on the bottoms of both the green LED and the blue LED are mounted on one of these lead frames so as to be in contact (see Japanese Laid-Open Patent Application 2003-17753, for example). With this light emitting device, this configuration improves the color mixing of the light of these colors while also affording a compact size.
However, when a light source featuring light emitting elements such as these is driven under harsher conditions, such as when the drive speed is raised, the brightness of the light emitting elements is increased, or the device is used for extended periods, the heat generated by the driving of the light emitting elements themselves shifts the wavelength of the light emitted from the light emitting elements. In particular, when light emitting elements that generate a large enough quantity of heat to become a heat source and light emitting elements whose wavelength fluctuates over a wide range are mounted in contact on the same substrate and/or on the same layer, color becomes unbalanced as the temperature rises. This loss of color balance leads to a critically adverse effect due to minute fluctuations in characteristics, as in optical printer devices and scanners that sense by using electrical and optical characteristics.